The revamped flipped string model gauge symmetry is \([SU(5)\times {U(1)}]\times {U(1)}^4\times {[SO(10)}\times {SU(4)]}\) .
As explained in Appendix A, the abelian factor product \({U(1)}^4\)  can be recast in the form \(\left\lbrace \prod _{I=1}^3{U(1)}_I^{\prime }\right\rbrace \times {U(1)}^{\prime }_A\) , where \(U(1)^{\prime }_I, I=1,2,3\)  are anomaly free and \(U(1)^{\prime }_A\)  is anomalous. The anomalous abelian symmetry is broken via the Dine-Seiberg-Witten mechanism at the loop level [1]}, involving therefore a VEV of the dilaton field, i.e. the string coupling. The induced Fayet-Iliopoulos term breaks supersymmetry unless it is cancelled by a VEV along
an appropriate matter field combination.
In this case, the D-flatness conditions associated with the \({U(1)^{\prime }}^4\)  group factor read [2]}, [3]}:
\({\cal D}_I &= \sum _{i} q^i_I \left|\varphi _i\right|^2=0\,, I=1,2,3\,,\\{\cal D}_A &= \sum _{i} q^i_A \left|\varphi _i\right|^2+\frac{1}{192\pi ^2}{2\alpha ^{\prime }}\,{\rm Tr}Q_A=0\,,\) 
